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Researchers investigating movement of black bears into new habitats

Minnesota black bears are expanding their range out of forested areas into farmland, leading state Department of Natural Resources researchers to study how and why these bears are adapting to a new habitat.

The department estimates Minnesota's bear population at 20,000. When food became scarce in forested areas to the east in the mid-1990s, black bears began moving into northwest Minnesota, DNR bear biologist Dave Garshelis said.

Researchers cannot yet say what percentage of the state's bears may be in northwestern Minnesota, but they're performing winter den checks to gather information.

During a recent outing in rural Marshall County, Garshelis and other researchers hiked down a snowmobile trail, then used snowshoes to head through the woods to the den.

"It looks like what happened is the bears settled out here and they're very prolific, the most prolific bears in Minnesota," Garshelis said. "Because there's good food. So the population here is actually going up.

Preparing to implant monitorMPR Photo/Ann Arbor Miller

"Most of the rest of the state is stable and we have an increasing population in this northwestern fringe of the bear range."

The research project is designed to learn where bears travel and what they eat.

As he neared the den, Garshelis called for silence. A female bear was hibernating, but she was still alert and might have been spooked by human voices.

After researchers cleared snow away from the opening of the den -- a hole in the ground under a fallen tree -- they listened for signs the bear might be agitated. But the only sound was of cubs noisily nursing.

A researcher crawled into the den to give the mother a shot that would sedate her for about an hour.

Bear cubMPR Photo/Ann Arbor Miller

"Basically we'll just check on her general health," said graduate student Mark Ditmer, as he waited for the sedative to take effect. "Check on her fat thickness. Just see how good a condition she's in."

Researchers pulled two cubs from the den. Born in mid-January, each was about the size of a house cat. The cubs were tucked into the researchers' coats to keep them warm.

Next, they pulled the sedated mother from the den to give her a battery of medical tests. She was measured and weighed. They also adjusted a global positioning system collar installed last summer to track her movements.

Researchers also pulled a chunk of hair from the bear's back. Garshelis said that by analyzing the hair they can learn important details about the bear's diet.

"We have a hair sample and you can tell from the hair sample whether she's been eating corn or not," he said. "That's an important thing we're looking at to see the variation among bears in how much corn they have in their diet."

Bears can smell ripe corn or oil seed sunflowers for miles and will gorge on those crops in the fall, he said.

Corn and oil seed sunflowers are likely a key reason bears are doing so well in this habitat where less than 20 percent of the land is forest.

Bears typically rely on native foods like acorns and berries.

"The bears actually prefer natural foods," Garshelis said. "But if those foods fail then they have corn and sunflowers as a backup. That's here every year. The risk for the corn and sunflowers of course is that they're going to get shot in a farmer's field."

Bears foraging in sunflower or corn fields can cause a lot of damage.

Many farmers are increasingly frustrated when crops are destroyed, Ditmer said. As a result, as the bear population in northwest Minnesota continues to expand, more conflicts with humans are likely.

At least one bear has moved nearly to North Dakota, where there are only fragments of forest among the farm fields.

Ditmer said the bear researchers are studying travel in a larger territory than any other black bears in North America. He said it's still not clear how far they will expand into the Red River Valley farmland.

"We're learning a lot in terms of what is the minimum threshold a bear can survive on and what [are] the minimum requirements they need," he said. "It will rewrite how we look at what's considered livable habitat for bears."

Currently Minnesota does not limit how many bears hunters can shoot in the northwestern part of the state.

But the DNR may soon place limits on how many bears hunters can kill to help protect and manage the growing bear population.